Ohio State researchers discovered that the long-term effects of breathing polluted air can cause changes in the brain as well as damage to the heart and lungs.
“The results suggest prolonged exposure to polluted air can have visible, negative effects on the brain, which can lead to a variety of health problems,” said Laura Fonken, lead author of the study and a doctoral student in neuroscience.
“This could have important and troubling implications for people who live and work in polluted urban areas around the world.”
The study appears online this week in the journal Molecular Psychiatry.
In previous studies in mice, researchers found that fine air particulate matter causes widespread inflammation in the body, and can be linked to high blood pressure, diabetes and obesity.
This new study aimed to extend their research on air pollution to the brain.
“The more we learn about the health effects of prolonged exposure to air pollution, the more reasons there are to be concerned,” said Randy Nelson, co-author of the study. “This study adds more evidence of pollution’s negative effects on health.”
In the new study, mice were exposed to either filtered air or polluted air for six hours a day, five days a week for 10 months – nearly half the lifespan of the mice.
The polluted air contained fine particulate matter, the kind of pollution created by cars, factories and natural dust. The fine particulates are tiny – about 2.5 micrometers in diameter, or about 1/30th of the average width of a human hair. These particles can reach deep areas of the lungs and other organs of the body.
The concentration of particulate matter that the mice were exposed to was equivalent to what people may be exposed to in some polluted urban areas, according to the researchers.
After 10 months of exposure to the polluted or filtered air, the researchers performed a variety of behavioral tests on the animals.
In a learning and memory test, mice who breathed the polluted air took longer to learn essential behaviors related to survival and were less likely to remember key behaviors.
In another experiment, mice exposed to the polluted air showed more depressive-like behaviors (such as anxiety) than did the mice that breathed the filtered air.
In an effort to determine how air pollution can lead to these changes in learning, memory and mood researchers tested the hippocampal area of the mice brains.
“We wanted to look carefully at the hippocampus because it is associated with learning, memory and depression,” said Fonken.
Results showed clear physical differences in the hippocampi of the mice who were exposed to polluted air compared to those who weren’t.
The researchers looked specifically at branches that grow off of nerve cells (or neurons) called dendrites. The dendrites have small projections growing off them called spines, which transmit signals from one neuron to another.
Mice exposed to polluted air had fewer spines in parts of the hippocampus, shorter dendrites and overall reduced cell complexity.
“Previous research has shown that these types of changes are linked to decreased learning and memory abilities,” said Nelson.
In other studies, several of the co-authors of this study found that chronic exposure to polluted air leads to widespread inflammation in the body, which is linked to a variety of health problems in humans, including depression.
Again, researchers found evidence that the low-grade inflammation was evident in the hippocampus.
In mice that breathed the polluted air, chemical messengers that cause inflammation – called pro-inflammatory cytokines – were more active in the hippocampus than they were in mice who breathed the filtered air.
“The hippocampus is particularly sensitive to damage caused by inflammation,” Fonken said. “We suspect that the systemic inflammation caused by breathing polluted air is being communicated to the central nervous system.”
Source: Ohio State University